Unmyelinated C fibers transmit messages more slowly and their nerve endings spread over a large area. They help you feel dull aches difficult to pinpoint. From the spinal cord, signals head to the thalamus , which relays signals to areas of the cerebral cortex transforming messages into conscious experience. Once aware, you can decide to be more careful the next time you approach the door.
Pain depends both on the strength of the stimulus and the emotional state and setting in which the injury occurs. When messages arrive in the cortex, the brain can process them differently depending on whether you had a good day or just broke up with your girlfriend.
The cortex sends pain messages to the periaqueductal gray matter, which activates pathways that modulate pain. Pathways send messages to networks that release endorphins — natural opioids that act like the pain reliever morphine. Adrenaline produced during emotionally stressful situations also serves as a pain reliever.
Releasing these chemicals helps regulate and reduce pain by intercepting signals traveling through the spinal cord and brainstem. Although everyone has these brain circuits, how well they work and how sensitive they are influence how much pain someone feels. Endorphins act at multiple types of opioid receptors in the brain and spinal cord. Doctors can deliver opioid drugs to the spinal cord before, during, and after surgery to reduce pain.
Scientists are studying ways to electrically stimulate the spinal cord to relieve pain while avoiding the harmful effects of long-term opioid use. No single brain area is responsible for pain and itch perception. Emotional and sensory components create a mosaic of activity influencing how we perceive pain. Some successful treatments target the emotional component like meditation, hypnosis, cognitive behavioral therapy, and the controlled use of cannabis.
There is more to learn about how the brain and body detect and process touch and pain. The story so far shows the complexity and importance of the somatosensory system. This article was adapted from the 8 th edition of Brain Facts by Marissa Fessenden. Sandra Blumenrath Sandra H. Sandra lives in Silver Spring, Maryland, with her husband, daughter, and a tank full of fish. Garibyan, L. But this is a simplification. The sensation of actual touch—something in contact with the skin—is picked up by specialized receptor structures and conveyed by specific nerve fibers to the brain.
There are separate but parallel receptors and nerve pathways for the sensations of temperature, body position and movement, and pain. Think of this group of senses as subsystems within the somatosensory system—members of a family that are closely related but unique and independent.
While receptors for the other senses are localized in compact sense organs the ears for hearing, the eyes for sight, the nose for smell , receptors for touch and its kindred senses are distributed all over the skin and inside the body. Many of these receptors are essentially nerve endings encapsulated in the cells of surrounding skin, muscle, or other tissue that have been modified into structures to convey physical forces pressure, stretching, motion to them.
Stimulating these mechanical receptors allows the flow of charged particles into the nerve, transforming the physical force. Other nerve endings in the system respond to changes in their chemical environment chemoreceptors or to temperature thermoreceptors.
These receptors are quite specialized. One type of touch receptor responds to a light brushing contact with the skin, another to firmer touch, others to hard pressure and to vibration.
There are at least six different thermoreceptors, each tuned to its own temperature range, from cold to warm to hot. The somatosensory system also includes receptors and neurons that convey information about body position and movement to the brain. These proprioceptors are housed in muscle, bone, and tendons and respond to stretch and contraction, tension and release. Pain is a member of the somatosensory family, with a difference: the other senses carry data about the external and internal environment that may or may not need prompt attention.
Pain is primarily a protective system whose signals are hard to ignore. Although pain is often the reaction to a physical extreme of temperature, pressure, twisting force on a joint, muscle contraction , it is not registered by the usual receptors for that sensation but by specialized nociceptors.
These are bare nerve endings that are activated by mechanical force or by chemicals released by damaged or inflamed tissue. Nociceptors are specialized, too: different ones respond to different kinds of tissue injury or distress, to register sharp, dull, or aching pain. Visceral nociceptors, buried in the internal organs, convey painful sensations that warn of disease.
Nerve impulses carrying somatic sensations travel along fibers peripheral nerves to the cell bodies of their respective neurons, which are located near the spinal cord. There, the release of neurotransmitters passes the signal along to fibers of the spinal cord itself, which run up to the brain.
Throughout this process, signals from the diverse types of sensation remain separate, traveling via parallel pathways. For most of these signals, the primary destination in the brain is the somatosensory cortex, a wide strip of the most evolved part of the brain that runs across the top of the brain from ear to ear.
Here and through connections with other brain regions, the myriad sensations of touch, temperature, and proprioception finally come together to be integrated into coherent, conscious experience—the perception of the physical self and its immediate contact with the world around it.
The mapping tactile of responses can sometimes aid clinical assessment. Sensory losses with clear regional boundaries indicate trauma to spinal nerves. For example, sensory loss along a dermatomal boundary can permit a reasonably precise determination of the affected spinal nerve or nerves Martini and Welch, Sensitivity to light touch in a particular area can be checked using gentle contact with a fingertip or a wisp of cotton wool.
The two-point discrimination test is used to generate a more detailed sensory map of tactile receptors. Two fine points of a drawing compass, a bent paperclip or other object are applied to the skin surface simultaneously and the subject is asked to describe the contact.
When the points fall within a single receptive field, the subject will report only one point of contact. A normal individual loses two-point discrimination at about 1mm on the surface of the tongue, 2—3mm on the lips and 3—5mm on the backs of the hands and feet and at 4—7mm over the general body surface Martini and Welch, Vibration receptors can be tested by applying the base of a tuning fork to the skin.
Damage to an individual spinal nerve produces insensitivity to vibration along the paths of the related sensory nerves. If the sensory loss results from spinal cord damage, the injury site can typically be located by walking the tuning fork down the spinal column, resting its base on the vertebral spines Martini and Welch, A number of terms are used to describe the level of sensitivity in an area of the body.
Anaesthesia means a total loss of sensation — the individual cannot perceive touch, pressure, pain or temperature sensations from that area. Allan, D. In: Montague, S. Edinburgh: Elsevier. Hancock, E. John Hopkins Magazine; 3. Marieb, E. Martini, F. Ewing, NJ: Benjamin Cummings. Sign in or Register a new account to join the discussion.
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